Effects of Li content on structure and electrochemical properties of Li1+x (Ni0.5 Mn0.5) 1-x O2 (0≤x≤0.15) electrodes in lithium cells (1.0-4.8 V)

Layered Li1+x (Ni0.5 Mn0.5) 1-x O2 (0x0.15) materials have been synthesized using Li2 CO3 and coprecipitated (Ni0.5 Mn0.5) (OH) 2. The materials with increased lithium content (x0.10) showed distinct differences in particle morphology, which is attributed to the melting of excess Li2 CO3 during calcination. The powder XRD patterns and the initial charging curves to 4.8 V indicated that the excess lithium resides in the transition metal layer to form Li2 MnO3 -like domains in the electrode structure such that these compounds can be reformulated in a two-component composite notation as 2x Li2 MnO3 (1-3x)Li (Niy Mn1-y) O2 (y=(1-x)[2(1-3x)]) with some cation disorder between the two components. The excess lithium significantly affected the charge/discharge behaviors in the low-voltage range (<2 V) and the rate capability of the electrode materials, which is attributed to increasing Ni3+ content and decreasing LiNi disorder (i.e., Ni content in the lithium layer) in the materials.